Origin of some gem minerals in Sri Lanka: evidence from corundumspinel-scheelite-taaffeite-bearing rocks

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The Ratnapura and Elahera gem fields of Sri Lanka have been renowned for their high quality gemstone for centuries. An improved understanding of the origin of gem minerals does not only have important regional geologic implications, but is also of economic significance. This paper presents the origin of some important gem minerals at Bakamuna (a known gem field in the vicinity of Elahera) and at Rupaha (a particularly unknown area for gems), on the basis of field and petrographical evidence and geochemical characteristics. Silica-undersaturated gem mineral-bearing reaction zones have been formed due to the reaction of chemically dissimilar rocks under high-temperature conditions in both localities. The high-temperature crustal metasomatism was followed by different kind of fluid infiltrations, which carried heavy metals to the higher crustal levels, and formed economically important minerals like scheelite.